1. Field of the Invention
The present invention is based on the Japanese Patent Application No. 2003-343442 applied on Oct. 1, 2003.
The present invention relates to a shaft-misalignment-measuring device which measures the misalignment of two shafts having a clutch engaged thereto; a shaft-misalignment-measuring method; a single-shaft combined plant employing the shaft-misalignment-measuring device; and a start-up method of the single-shaft combined plant.
2. Description of the Prior Art
In recent years, a single-shaft combined plant having a gas turbine connected directly to a steam turbine with one shaft serves as a combined plant of high efficiency which can flexibly respond to a change of electrical consumption amount per day, emitting a little amount of toxic substances such as NOx. Conventionally, a single-shaft combined plant constructed in the above-mentioned manner actuates a gas turbine and a steam turbine simultaneously. Therefore, in order to start up both turbines simultaneously, a larger start-up torque is required, thereby needing a thyristor that can generate this huge start-up torque.
Additionally, it is necessary to supply cooling steam to the steam turbine so as to prevent the temperature of the steam turbine blades from increasing excessively due to windage loss. However, steam to be supplied to the steam turbine cannot be generated by a heat recovery steam generator which generates steam by using the exhaust gas of a gas turbine until the electrical output of a generator rotated by a gas turbine is increased. Therefore, an auxiliary boiler is necessary which has an enough capacity to supply sufficient cooling steam to the steam turbine. Further, in a conventional single-shaft combined plant, it is necessary to place a gas turbine, a steam turbine and a generator in a line and an axial-flow exhaust type of steam turbine cannot be applied. Therefore, it is necessary to install a condenser under the steam turbine. As a result, it is necessary to install a gas turbine, a steam turbine and a generator on a higher level, which requires a turbine plant building to be constructed so as to have a plurality of floors.
In order to solve these issues, such a single-shaft combined plant as shown in FIG. 11 is proposed that has a clutch 204 applied between a gas turbine 201 and a steam turbine 202. (Refer to the Japanese Patent Application Laid-Open No. 2003-13709.) The single-shaft combined plant shown in FIG. 11 has a generator 203 installed between the gas turbine 201 and the clutch 204. By applying a clutch 204 as described above, it is possible to connect and disconnect a gas turbine 201 and generator 203 and a steam turbine 202. Consequently, at the start-up time, first, only the gas turbine 201 and the generator 203 are started up in a condition that the gas turbine 201 and generator 203 are disconnected from the steam turbine 202 by the clutch 204. Then, when the steam generated in an heat recovery steam generator (not illustrated herein) can be supplied to the steam turbine 202, the steam is introduced into the steam turbine 202 so as to start up the steam turbine 202. After that, when the steam turbine 202 attains the rated rotation speed, the gas turbine 201 and generator 203 will be connected to the steam turbine 202 by the clutch 204, thereby having the torque of the steam turbine 202 transmitted to the generator 203.
Because in a single-shaft combined plant to which this clutch 204 is applied, it is necessary to first start up the gas turbine 201 and the generator 203 only at the beginning of the start-up time, it is possible to make the capacity of a thyristor necessary for start-up small. Also, while only the gas turbine 201 and the generator 203 are being started up, the steam turbine 202 is rotating at a low speed, thereby requiring no cooling steam. As a result, it is possible to make the capacity of an auxiliary boiler small. Additionally, because the thermal expansion of the steam turbine 202 can be absorbed by the clutch 204, it is possible to construct a single-shaft combined plant so as to have a gas turbine 201, a generator 203 and a steam turbine 202 line sequentially in the aforesaid order as shown in FIG. 11, thereby making it possible to place the steam turbine at one end. Consequently, because the steam turbine 202 can be an axial-flow exhaust steam turbine, it is possible to employ an axial-flow exhaust condenser, thereby making it unnecessary to place a turbine shaft on a high level as is conventionally placed.
As described above, because at the start-up time, a single-shaft combined plant provided with a clutch 204 as shown in FIG. 11 has the steam turbine 202 actuated after the gas turbine 201 is started up, the gas turbine 202 has been rotating at the rated rotation speed for a long time before the start-up of the steam turbine 202. Consequently, the bearing pedestals on the side of the gas-turbine 201 of the clutch 204 are expanded due to high bearing drain oil temperature, whereas the bearing pedestals on the side of the steam turbine 202 of the clutch 204 have a different expansion ratio which depends on the state of the steam turbine 202.
In other words, when the steam turbine 202 is shut down with the condenser vacuum maintained, gland steam is flowing to the bearings of the steam turbine 202 for a long time. As a result, the bearing pedestals on the side of the steam turbine 202 are slightly expanded. However, because the gland steam does not flow to the bearings of the steam turbine 202 when the steam turbine 202 is stopped with the condenser vacuum broken, the bearing pedestals on the side of the steam turbine 202 are approximately in an initial state and are not expanded. Further, because the steam turbine 202 hardly rotates before the steam turbine 202 is started up, the bearing pedestals on the side of the steam turbine 202 do not have such a large expansion ratio as the bearing pedestals on the side of the gas turbine 201.
At the start-up time, in a single-shaft combined plant equipped with a clutch 204 configured as described above, the expansion ratio of the bearing pedestals on the side of the gas turbine 201 differs from the expansion ratio of the bearing pedestals on the side of the steam turbine 202 and this difference in expansion ratio also differs, depending on the state of the steam turbine 202. Further, not only the expansion ratio differs between the bearing pedestals of the gas turbine 201 and the bearing pedestals of the steam turbine 202 but also the lifting amount and the inclination of the shafts of the gas turbine 201 and the steam turbine 202 differ. As a result, there arises a misalignment between the center of the shaft of the gas turbine 201 and the center of the shaft of the steam turbine 202.
The amount of this misalignment between the center of the shaft of the gas turbine 201 and the center of the shaft of the steam turbine 202 gives an influence when the gas turbine 201 and generator 203 are connected to the steam turbine 202 by engaging the clutch 204 at the start-up time. In other words, because the clutch 204 is engaged in a condition that the gas turbine 201 and generator 203 and the steam turbine 202 are rotating nearly at the rated rotation speed, when the amount of misalignment between the center of the shaft of the gas turbine 201 and the center of the shaft of the steam turbine 202 becomes larger than a predetermined designed value, there is a possibility that an excessive stress is applied to the clutch 204, resulting in a breakage of the clutch 204.